The control of light artifically supplied to certain indoor and outdoor areas can involve a great deal of complexity. In this regard, it is not unusual for a light control system to employ a computer, especially when lighting is controlled in a number of areas at the same time. A good example of this kind of situation is light control in various offices and/or floors of a high-rise office building. The computer turns on, dims, or shuts off lights in specific work areas depending on the amount of natural lighting available in each. During a bright, sunny day lights may be turned off because sufficient natural light from the sun is available through windows or skylights. On the other hand, on a cloudy, dark day the computer would recognize the need for lights and would control them accordingly.
A separate light sensor is used to sense the amount of light in each regulated area. For example, in an office building there would be a number of regulated areas corresponding to the various offices located on different floors and on different sides of the building. Each sensor is connected to the system's computer which monitors the sensor's output. The kind of computer generally used in this application is an analog computer, which is typically designed to operate at certain low voltage and current levels. For example, a typical analog computer may be designed to receive signal inputs within the range of either 1 to 5 volts DC, or 4 to 20 milliamps. In the past, light sensors did not or could not output accurate signals compatible with these voltage and current level requirements.
It should be appreciated, and as a person skilled in the art would know, in a light control system it is important that sensor output accurately reflect the amount of light sensed. Sensors that use photodiodes, for example, output an electrical signal that corresponds to a voltage across the photodiode, which changes correspondingly with varying amounts of light received. This voltage and power output is low in magnitude. Since the sensor is usually physically located a significant distance from the computer, a photodiode's output cannot be directly transmitted to the computer over a wire without picking up significant electrical noise that impairs the signal. To overcome this, light control engineers have designed sensors that have an amplifier mounted in the sensor head. The amplifier outputs a signal at a higher voltage and/or current level that corresponds to the light measured by the photodiode. The higher voltage and/or current level makes the signal less susceptible to noise pickup and the signal can be transmitted relatively unimpaired. The trade-off is that although higher voltage or current is desirable for transmitting sensor output down a wire, it is by necessity too high to be compatible for direct input to the typical computer. Therefore, past practice has been to use additional gain control and conditioning circuitry that is remotely located from the sensor head but near the computer. This additional circuitry reduces and alters the sensor head's electrical output to compatible levels. This is the kind of system disclosed by me in U.S. Pat. No. 4,647,763 which issued on Mar. 3, 1987. Although it has its advantages from the standpoint that it permits conveniently accessible sensor head gain control at a single location for all sensors in a system, it has a significant disadvantage in that the requirement for remotely located gain control and conditioning circuitry adds significant expense to a light control system. I have solved this problem by developing a self-contained sensor head that has the unique capability of outputting a compatible signal directly to a computer.